This research is a clinical study in which humoral and cell-mediated immune (CMI) responses of humans, to varicella-zoster (V-Z) virus will be examined. These functions will be related to the presence or absence of infection with V-Z virus, to recovery from V-Z infections and to reactivation of latent V-Z infection. Immune responses of normal and immunocomprised persons will be compared to try to establish what deficiencies exist in the latter. The susceptibility of white blood cells (WBC) of such persons to support the growth of V-Z virus will also be studied. Antibody to V-Z virus will be measured by indirect immunofluorescence (FAMA) and immune adherence hemagglutination (IAHA). Long-term prospective studies of V-Z antibody titers in patients immune to varicella will be performed to see whether decreases in titer occur prior to reactivation of latent V-Z infection. CMI to V-Z virus will be studied by a technique whereby the inactivation of V-Z virus by WBC from persons immune to varicella is assayed (no inactivation is seen with WBC from susceptibles). The mechanism by which immune WBC inactivate V-Z virus will be examined. The roles of T and B lymphocytes and macrophages in V-Z virus inactivation will be determined.